The effects of sulphur dioxide and ozone on the mycorrhizas of Scots pine and Norway spruce in a field fumigation system

The work described below was performed in an open air fumigation experiment in which young conifers were exposed to controlled levels of the pollutant gases sulphur dioxide (SO₂) and ozone (O₃). The mycorrhizal community was analysed both by fruitbody counts and root harvests for morphotype analysis throughout the 6 yr of the experiment. Above ground there was a classical fruit-body succession from nursery species to a mixed community dominated by Suillus spp. under Scots pine and Cortinarius spp. under Norway spruce. Below ground there were changes in the morphotype community structure with time, but no similarity between the morphotype and fruit-body data. There were no effects attributable to SO₂ or O₃ on the mycorrhizal community above or below ground, but multivariate analyses suggested that the fruit-body succession was more advanced in plots with low levels of available phosphate.